The present invention relates to nozzles through which a flow of particles passes and more particularly to improving the durability thereof.
Internal combustion engines designed to achieve a useful power output through the controlled combustion of solid powdered fuels, such as coal, have been proposed essentially since the early investigations of Rudolph Diesel. Generally, the difficulties encountered by investigators in connection with these engines have centered about the development of techniques for forming and controlling a particulate fuel-air mixture for introduction in properly timed fashion into a combustion chamber.
In one engine design approach, a mixture of powered coal and air is conveyed to an intake manifold, pre-combustion chamber, or the like, whereupon the mixture is directed to a combustion region for admission. The maintenance of the particulate suspension during this procedure is difficult, resulting in unwanted powder accumulation and degradation of desired fuel-air ratios. Approaches intended to maintain a proper particulate suspension have included, for example, "animators" serving to agitate particles within the mixture as it awaits introduction to a region of combustion. Loss of consistency in a predetermined and desired suspension necessarily results in a loss of accurate metering of fuel into the combustion chamber leading to vagaries in cylinder power output. The coal/air mixture is pumped into the combustion chamber under pressure, thus creating nozzle erosion problems, particularly with the orifice of the nozzle that injects the mixture in the combustion chamber.
In another typical engine design approach, a mixture of coal and water (hereinafter sometimes referred to as CWM") is injected into a compression ignition reciprocating internal combustion engine such as a large, medium-speed, multi-cylinder diesel engine. In such a mixture, there are fine particles of coal which similarly can cause excessive rates of wear and premature failure of components in the fuel injection system. CWM fuel includes, for example, from less than 30 wt-% to as much as 60 wt-% coal particles in the range of from 0.01 to 50 microns in diameter. These particles are both abrasive and corrosive to the materials used in the nozzles and other components of the fuel injection system.
Regardless of the form of the fuel mixture, rapid wear of the fuel injection nozzle due to erosion is a universal problem. Solutions thereto, particularly with respect to CWM fuel, have included the insertion of a bushing or liner of very hard material in the nozzle of the fuel injector. These liners have been manufactured from silicon carbide, cubic boron nitride, tungsten carbide, polycrystalline diamond compacts, and alumina (sapphire). While some of these materials appear as appropriate candidates for CWM nozzle orifice applications, such liners undesirably affect the flow, atomization and strength characteristics that are required for proper operation of the fuel injection system.